Method of dosing vapor-discharge lamps with gallium



Nov. 17, 1970 K. T. PRZYBILLA 3,540,789

METHOD OF DOSING VAPOR-DISCHARGE LAMPS WITH GALLIUM Filed April 8, 1968 TO PUMP PUMP T I N VENTOR.

KARL T. PRZYBILLA AGENT Uitecl States Patent U.S. Cl. 316-24 4 Claims ABSTRACT OF THE DISCLOSURE The present invention deals with a method of dosing vapor-discharge lamps of the metallic-additive type with gallium by mixing mercury and gallium in a vacuum mixing chamber in amounts calculated to provide a stock amalgam in a determined mercury-gallium ratio not exceeding 3 parts gallium to 100 parts mercury by weight. A predetermined small amount of the stock amalgam of determined mercury-gallium ratio is further mixed with a predetermined amount of additional mercury to provide a lamp dosing amalgam having between about M03300 to weight percent gallium to mercury. The dosing amalgam and a predetermined amount of mercury halide or a halogen are placed in a vacuum feed chamber communicating with the interior of a lamp envelope and therefrom fed into the lamp envelope.

BACKGROUND OF THE INVENTION In a metallic-additive type vapor discharge lamp dosed with gallium as the additive metal, it is important that the lamp is dosed with an exact amount of gallium for the particular size and rating of the lamp. If the gallium is added in too great an amount, the arc discharge will not provide uniform radiation over the length of the are. In such case there is a greater gallium radiation at or near the electrodes than in the center of the are. On the other hand, if the gallium additive is too little, there will be insuflicient arc radiation in the diazo range (320-450 nanometers) for certain photoprinting purposes. If the gallium content is substantially precise, then there is uniform radiation over the length of the arc.

The relatively small amounts of gallium which are required for optimum lamp performance (0.1 mg. and less) constitute a severe difliculty so far as accurate dosing is concerned. Gallium is very brittle when solid and liquidizes at approximately 29 C. Unlike mercury, gallium, when liquid, sticks to the quartz lamp vessel and cannot be moved even by torching, to another part of the vessel.

SUMMARY OF THE INVENTION In accordance with the invention it has been found that it pure gallium, (e.g., 99.999% pure), is dissolved in clean, e.g. distilled, mercury in the ratio of not more than 3 parts gallium to 100 parts mercury by weight, preferably 1.0% gallium by weight to mercury, or less, then the formed gallium amalgam can be driven from one location in a container to another location as easily as pure mercury, dosing is very easy and reliable and can be introduced by a syringe as the dosing instrument with the accuracy of the dosing being limited only by the type of syringe used, e.g., a micro-syringe, and the gallium amalgam can be easily kept clean and free from oxidation as long as it is kept in an inert atmosphere. The mixing of the gallium and mercury is accomplished in a vacuum mixing chamber to provide a stock amalgam of determined mercury-gallium ratio, which is removed from the vacuum mixing chamber and kept under an inert atmosphere, from which a dosing amalgam is prepared by add- I "ice ing sufficient mercury to a determined amount of the amalgam to provide a dosing amalgam containing between about to O Weight percent gallium to mercury. The dosing amalgam and a predetermined amount of mercury halide or a halogen is placed in a vacuum feed chamber communicating with the interior of a lamp envelope under vacuum and therefrom fed into the lamp envelope with the subsequent addition of an ionizable starting gas, e.g., argon, introduced into the lamp envelope through the vacuum feed chamber.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an elevational side view of a vacuum mixing chamber employed in the method of the invention,

FIG. 2 illustrates a stem portion removed from the chamber of FIG. 1, and

FIG. 3 illustrates an elevational side view of a vacuum feed chamber communicating with a lamp envelope in the practice of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the prcatice of the invention, there is provided a vacuum mixing chamber preferably of quartz in the form of a tube 1 closed at one end 2 and having a pair of side stems 3 and 4, each closed at one end 5 and 6, respectively, spaced from each other axially of the tube 1 and communicating with the interior of the tube 1. A vacuum pump (not shown) is connected to the open end of tube 1 by means of tubing 7 and the chamber is vacuum degassed to remove any impurity gases in the chamber. Thereafter, the side stems are broken off intermediate their ends, as at 8 and 9, and a weighed amount of pure gallium 10, e.g., 1 gram of gallium, is deposited in the removed portion of one of the stems, e.g., side stem 3, and a weighed amount of pure mercury, e.g., 100 grams mercury 11, is deposited in the other removed portion, e.g., side stem 4. The portions are than re-se aled to their respective stems, e.g., by heat fusion, and the chamber is again evacuated to less than about 10 mm. Hg to provide a suitable vacuum therein. During the application of vacuum, the gallium-containing side stem is heated to about 1000 C. to drive off any possible impurity and the tube 1 is sealed off, as at 12, thereby maintaining the chamber under vacuum. The sealed vacuum chamber is then manipulated by turning it and inclining it to cause the mercury 11 to leave stem 4 and enter stem 3 where it is mixed with the gallium by shaking while heated to about C. until the gallium dissolves in the mercury to form an amalgam. Mercury and gallium are to a degree mutually soluble as evidenced by Spicer et al., pages 868- 9, Journal of the American Chemical Society 73, 1951. The amalgam containing side stem 3 is then removed by breaking it off as at 8 and the broken-01f portion as illustrated by FIG. 2, now contains the amalgam 13 as a stock amalgam and is stored in an inert atmosphere for subsequent dilution with additional mercury to provide the dosing amalgam.

Referring to FIG. 3, the lamp to be dosed with the gallium amalgam can be any suitable vapor discharge lamp, such as illustrated, which shows a lamp envelope 34 of light-transmitting fused quartz containing main operating electrodes 14 and 15 connected, respectively, to lead-in conductors 16 and 17 through sealed ends 18 and 19 having sealed therein ribbon-type seals 20 and 21 intermediate the electrodes and lead-in conductors. Conventionally, the lamp may also contain a starting electrode 22 positioned adjacent electrode 15 and connected to a lead-in conductor 23 through a ribbon seal 24, as illustrated. Extending from a side of envelope 34 is a feed chamber in the form of a tube 25 communicating at one end with the interior of the lamp envelope. The feed chamber is provided with a pair of side stems 26 and 27 spaced from each other axially of the tube 25 and having its other end connected to a vacuum pump (not shown) by means of tubing 28. Portions 29 and 30 of the side stems 26 and 27 are removed, e.g., by breaking-off as at 31 and 32. Into the removed portion.30 of side stem 27 is deposited a measured amount of a mercury halide or a halogen, e.g., mercury iodide, depending upon the lamp rating and volume. Into the removed portion 29 of side stem 26 is deposited by means of a micro-syringe a small amount of the stock amalgam, e.g., having a mercury-gallium ratio of 1 part gallium to 100 parts mercury by weight, to which is added additional pure mercury, to arrive at the dosing amalgam containing, for example, 1 weight percent gallium to mercury. The dosing amalgam is calculated in accordance with the lamp rating and volume.

For example, for a lamp having an operating wattage of 2,200 watts and a volume of 190 cm. a micro-syringe removes 3 mg. amalgam from the stock amalgam and a further 883 mg. of pure mercury from a source of pure mercury which is then deposited into the removed portion 29 of the stem 26. The amount of mercury iodide deposited in portion 30 for this lamp is 0.3 mg. mercury iodide. The portions 29 and 30 are then rescaled to their respective stems and, while under the application of vacuum, stem 26 is heated to from about 100 C. to about 400 C. and stem 27 is heated to from about 120 C. to about 200 C. to prevent any possible moisture from the lamp envelope from entering the side stems. The lamp and feed chamber are vacuum degassed to less than about l mm. Hg to remove any impurity gases, while the lamp envelope is heated between about 400 C. to about 1,000 C. While under the application of vacuum anionizable starting gas, such as argon, is introduced into the lamp envelope through the feed chamber according to known procedure, for example, as described in Pat. No. 3,279,877. Thereafter, the feed chamber 25 is heat sealed as at 33 while under vacuum. In the vacuum-sealed condition, the lamp and feed chamber are manipulated to cause the dosing amalgam and mercury iodide, preferably under heat application, to pass from the side stems into the lamp envelope. The feed chamber is then sealed oif near the side of the envelope 34 and removed.

Various modifications of the invention are contemplated within the scope of the appended claims.

What is claimed is:

1. The method of dosing a vapor-discharge lamp with gallium amalgam comprising mixing gallium and mercury in a vacuum mixing chamber in amounts calculated to provide a stock amalgam in a predetermined mercurygallium ratio not exceeding 3 parts gallium to parts mercury by weight, removing the stock amalgam from the vacuum mixing chamber, adding a predetermined amount of additional mercury to a predetermined amount of the stock amalgam to provide a lamp dosing amalgam having between to 6 Weight percent gallium to mercury, depositing the dosing amalgam and a predetermined amount of a material selected from the group consisting of a halogen and a mercury halide in a vacuum feed chamber connected to a lamp envelope and communicating with the interior of the lamp-envelope, applying heat and vacuum to the vacuum chamber, while under the application of vacuum, passing a predetermined amount of a starting gas into the vacuum feed chamber and into the lamp envelope through the vacuumfeed chamber, thereafter sealing Off an end portion of the vacuum chamber remote from the lamp envelope, feeding the said material and the dosing amalgam from the vacuum feed chamber into the lamp envelope, and sealing OE and then removing the feed chamber from the lamp envelope.

2. The method according to claim 1, wherein the mercury halide is mercury iodide.

3. The method according to claim 1, comprising mixing 1 gram of gallium and 100 gramsmercury in the vacuum mixing chamber to provide a stock amalgam, and shaking the mixture under application of heat until the gallium dissolves in the mercury.

4. The method according to claim 2, comprising applying vacuum to the feed chamber while heating the mercury iodide and the dosing amalgam contained therein, and subsequently sealing the vacuum chamber from the applied vacuum.

References Cited UNITED STATES PATENTS 3,188,778 6/1965 Wiener et al 3l6--24 XR 3,279,877 10/1966 Smith et a1 316-24 XR 3,385,645 5/1968 Smith 3l6l6 H. A. KILBY, JR. Primary Examiner US. Cl. X.R. 

